In the past, cellular phones have been used as communication devices that transmit analog acoustic signals, i.e. voice and sound, from a handset to a cellular network. When a person speaks into the phone, the sound waves generated by the mouth are received by a microphone and converted into analog electrical signals, or waves. These electrical waves are then transmitted from the phone to a cellular tower, where they pass through the cellular network and are then routed to the recipient's phone. The electrical waves are then converted back into sound through a loud speaker. In this fashion, analog phones provide effective, reliable transmission of sound.
The advent of digital phones brought about a change in the transmission process. In a digital phone, the sound waves received by the microphone are encoded into a specific series of zeroes and ones called a "digital word". This encoding takes place in an "analog to digital" converter. The zeroes and ones are then sent to the cellular network in the form of radio waves, where they again pass through the tower and are sent to the recipient's phone. There they are decoded by a "digital to analog" converter. They then are converted to sound through the loud speaker.
Digital phones offer several advantages over their analog counterparts. First, digital signals are virtually immune to static noise. Static takes the form of analog waves that look to the phone like normal phone calls. In a digital phone, however, the phone call looks very different from the static. The phone is thus able to filter out the noise.
Second, cellular networks can fit many more digital signals into a wire than analog signals. Again, due to the sophisticated filtering in digital systems, a phone can easily distinguish it's digital call from that intended for another phone.
Finally, as computers also communicate with ones and zeroes, digital phones are able to receive more than just sound. For example, digital phones can receive pages, caller identification data, internet information, text, pictures and other information. The i1000 phone manufactured by Motorola, for instance, can receive text pages, voice mail, and caller identification data in addition to phone calls!
While these additional features of digital phones are great for the end user, they present some major obstacles for the battery charger designer. For example, chargers for some phones include charging algorithms which ramp and taper the voltage and current to charge a battery. Chargers for other phones, however, supply basic voltage to the phone, while charging circuitry inside the phone ramps and tapers the voltage and current. For these phones, where the charging circuitry located inside the phone, the phone must communicate it's charging state, i.e. one quarter charged, half charged, etc., to the charger. This information is needed by the charger because the charger lights an indicator depending -upon the charge state. For example, a green light on the charger might indicate a fully charged battery while a red light might indicate a charging battery.
Traditionally, this communication occurred through a data connector located on the bottom of the phone. When the phone was in the charger, the charger data connector mated with the phone data connector. The state of charge was communicated digitally across this interface. With the advent of digital communication features, many phones now come with accessories like global positioning systems that connect to the phone's data connector. If such an accessory is connected to the phone when the phone is inserted in the charger, the charger can no longer use this port for communicating charging information.
There is thus a need for an improved, simplified charging status indication means in telephone/charger systems.